Controller, control method and non-transitory storage medium storing control program thereon

Abstract

There is provided a controller for fitting first and second workpieces to each other using a robot. The robot has a gripping mechanism for gripping the first workpiece and a force sensor. The controller causes the robot to perform an operation of pressing the first workpiece against the second workpiece with a predetermined force, and an operation of changing a posture of the first workpiece with respect to the second workpiece in a state where the first workpiece is pressed against the second workpiece. The controller searches for the posture of the first workpiece in which a first surface of the first workpiece to be in contact with the second workpiece and a second surface of the second workpiece to be in contact with the first workpiece are parallel to each other, based on an evaluation index related to a distance between the first workpiece and the second workpiece.

What is claimed is: 
     
         1 . A controller for fitting a first workpiece and a second workpiece to each other using a robot, wherein
 the robot comprises a gripping mechanism for gripping the first workpiece, and a force sensor,   the controller is configured to cause the robot to perform
 an operation of pressing the first workpiece against the second workpiece with a predetermined force, and 
 an operation of changing a posture of the first workpiece with respect to the second workpiece in a state where the first workpiece is pressed against the second workpiece, and 
   the controller is configured to search for the posture of the first workpiece in which a first surface of the first workpiece to be in contact with the second workpiece and a second surface of the second workpiece to be in contact with the first workpiece are parallel to each other, based on an evaluation index related to a distance between the first workpiece and the second workpiece.   
     
     
         2 . The controller according to  claim 1 , wherein the evaluation index is a distance from a surface set in advance in the second workpiece to a measurement point set in a coordinate system with an arm tip end of the robot as a reference. 
     
     
         3 . The controller according to  claim 2 , wherein the measurement point is set such that, when the measurement point is projected onto a surface including the first surface, a projection position is present within a range defined by two outermost sides of the first surface to be in contact with the second surface in the operation of changing the posture of the first workpiece. 
     
     
         4 . The controller according to  claim 1 , wherein the evaluation index is a correction amount for instructions given to the robot, for pressing the first workpiece against the second workpiece with the predetermined force. 
     
     
         5 . The controller according to  claim 1 , wherein the controller is configured to determine a posture in which the evaluation index becomes an extreme value, as the posture of the first workpiece in which the first surface and the second surface are parallel to each other. 
     
     
         6 . The controller according to  claim 1 , wherein a reference point for controlling a position and a posture of the robot is set inside the first surface of the first workpiece. 
     
     
         7 . The controller according to  claim 1 , wherein
 the operation of changing the posture of the first workpiece with respect to the second workpiece comprises
 an operation of rotating the first workpiece in a first direction around an axis orthogonal to a direction in which the first workpiece is pressed against the second workpiece, and 
 an operation of rotating the first workpiece in a second direction that is an opposite direction to the first direction. 
   
     
     
         8 . The controller according to  claim 7 , wherein the controller is configured to determine an average of a first posture of the first workpiece determined by rotating the first workpiece in the first direction and a second posture of the first workpiece determined by rotating the first workpiece in the second direction, as the posture of the first workpiece in which the first surface and the second surface are parallel to each other. 
     
     
         9 . The controller according to  claim 1 , wherein
 the operation of changing the posture of the first workpiece with respect to the second workpiece comprises
 an operation of changing the posture of the first workpiece with respect to the second workpiece at a first change speed, and 
 an operation of changing the posture of the first workpiece with respect to the second workpiece at a second change speed different from the first change speed. 
   
     
     
         10 . The controller according to  claim 9 , wherein the second change speed is smaller than the first change speed. 
     
     
         11 . The controller according to  claim 1 , wherein
 the controller is configured to
 determine the posture of the first workpiece in which the first surface and the second surface are parallel to each other, based on a result of a search obtained by rotating the first workpiece only in a first direction around an axis orthogonal to a direction in which the first workpiece is pressed against the second workpiece, and 
 update the posture of the first workpiece in which the first surface and the second surface are parallel to each other, based on a result of a search obtained by rotating the first workpiece in the first direction and a result of a search obtained by rotating the first workpiece in a second direction that is an opposite direction to the first direction. 
   
     
     
         12 . The controller according to  claim 11 , wherein
 the controller is configured to
 rotate the first workpiece at a first change speed in a case of rotating the first workpiece only in the first direction, and 
 rotate the first workpiece at a second change speed smaller than the first change speed in a case of rotating the first workpiece in the first direction and the second direction. 
   
     
     
         13 . The controller according to  claim 1 , wherein the controller is configured to remove an offset based on force information output from the force sensor in a state where the first workpiece and the second workpiece are not in contact with each other. 
     
     
         14 . A control method for fitting a first workpiece and a second workpiece to each other using a robot, wherein
 the first workpiece is gripped by a gripping mechanism of the robot, and   the control method comprises
 pressing the first workpiece against the second workpiece with a predetermined force, 
 causing the robot to change a posture of the first workpiece with respect to the second workpiece in a state where the first workpiece is pressed against the second workpiece, and 
 searching for the posture of the first workpiece in which a first surface of the first workpiece to be in contact with the second workpiece and a second surface of the second workpiece to be in contact with the first workpiece are parallel to each other, based on an evaluation index related to a distance between the first workpiece and the second workpiece. 
   
     
     
         15 . The control method according to  claim 14 , wherein the evaluation index is a distance from a surface set in advance in the second workpiece to a measurement point set in a coordinate system with an arm tip end of the robot as a reference. 
     
     
         16 . The control method according to  claim 15 , wherein the measurement point is set such that, when the measurement point is projected onto a surface including the first surface, a projection position is present within a range defined by two outermost sides of the first surface to be in contact with the second surface in the operation of changing the posture of the first workpiece. 
     
     
         17 . The control method according to  claim 14 , wherein the evaluation index is a correction amount for instructions given to the robot, for pressing the first workpiece against the second workpiece with the predetermined force. 
     
     
         18 . A non-transitory storage medium storing thereon a control program for fitting a first workpiece and a second workpiece to each other, wherein
 the first workpiece is gripped by a gripping mechanism of a robot, and   the control program causes one or more processors to perform:
 giving instructions to the robot for pressing the first workpiece against the second workpiece with a predetermined force, 
 giving instructions to the robot for changing a posture of the first workpiece with respect to the second workpiece in a state where the first workpiece is pressed against the second workpiece, and 
 searching for the posture of the first workpiece in which a first surface of the first workpiece to be in contact with the second workpiece and a second surface of the second workpiece to be in contact with the first workpiece are parallel to each other, based on an evaluation index related to a distance between the first workpiece and the second workpiece. 
   
     
     
         19 . The non-transitory storage medium according to  claim 18 , wherein the evaluation index is a distance from a surface set in advance in the second workpiece to a measurement point set in a coordinate system with an arm tip end of the robot as a reference. 
     
     
         20 . The non-transitory storage medium according to  claim 19 , wherein the measurement point is set such that, when the measurement point is projected onto a surface including the first surface, a projection position is present within a range defined by two outermost sides of the first surface to be in contact with the second surface in the operation of changing the posture of the first workpiece.